A*HAR: A New Benchmark towards Semi-supervised learning for Class-imbalanced Human Activity Recognition
This addresses the problem of developing robust activity recognition systems for applications like healthcare, but it is incremental as it primarily establishes a benchmark.
The paper tackles the lack of semi-supervised learning benchmarks for class-imbalanced human activity recognition by introducing A*HAR, finding that Mean Teacher improves performance with limited labeled data but struggles with unbalanced activities.
Despite the vast literature on Human Activity Recognition (HAR) with wearable inertial sensor data, it is perhaps surprising that there are few studies investigating semisupervised learning for HAR, particularly in a challenging scenario with class imbalance problem. In this work, we present a new benchmark, called A*HAR, towards semisupervised learning for class-imbalanced HAR. We evaluate state-of-the-art semi-supervised learning method on A*HAR, by combining Mean Teacher and Convolutional Neural Network. Interestingly, we find that Mean Teacher boosts the overall performance when training the classifier with fewer labelled samples and a large amount of unlabeled samples, but the classifier falls short in handling unbalanced activities. These findings lead to an interesting open problem, i.e., development of semi-supervised HAR algorithms that are class-imbalance aware without any prior knowledge on the class distribution for unlabeled samples. The dataset and benchmark evaluation are released at https://github.com/I2RDL2/ASTAR-HAR for future research.